Liner bolts are typically used to secure sacrificial liners to the internal casing of mills used in the mining industry. The sacrificial liners are routinely replaced during maintenance of the mills. Typically such mills may range in size from three meters to eleven meters in diameter and are lined with replaceable heavy steel segments attached internally to the mill casing by through bolting using liner bolts. The liner bolts typically have a diameter of up to about 50 mm (2 inches).
In such applications, the bolts become corroded and clearances between bolts and holes become compacted with ore fines. This results in difficult bolt removal at liner removal time. As a result the many liner bolts that are utilized to attach the liners to the mill shell are often required to be freed manually by the use of large sledge-hammers. This is a difficult and time-consuming task that may result in injury to the workers.
While it is well known to use percussive devices such as jack-hammers and hydraulically powered hammers to provide repetitive impacts for many applications, they are not able to be manually guided into alignment with wall mounted bolts and other components. The applications of jack hammers are limited as the hammering effect produced by an electrically or pneumatically operated jack hammer does not provide the impact as would be provided by a sledge hammer, for example.
In known hammering devices capable of delivering such impacts, a high reaction force is produced which necessitates that such devices be carried by articulating machines or be rigidly attached to some support structure. This reduces their versatility and makes them unsuitable for many applications. Furthermore, it is difficult to quickly and accurately align such devices with the shank of a bolt or the like for effecting ready removal thereof.
International publication WO97/26116 (Russell Mineral Equipment Pty Ltd) describes a hydraulic liner bolt removal tool. The hydraulic tool essentially comprises a housing having a moil mounted at the forward end and a hydraulic piston assembly reciprocally moveable along the hammer axis between a striking position at which the piston assembly strikes the impact delivery member and a retracted position remote from the impact delivery member. A firing means is provided for hydraulically firing the piston assembly from its retracted position to its striking position under the control of actuating means. A reactive body assembly is moveable in the direction of the hammer axis by driving means towards the impact delivery member prior to operation of the firing means whereby the reactive body assembly may be energized by movement and subsequently decelerated to substantially absorb the reaction generated by firing the piston assembly. Recoil is thus reduced whereby the apparatus may be operated by hand with the apparatus being suspended about its centre of gravity at the work site.
U.S. Pat. No. 6,904,980 (Rubie) describes a pneumatic liner bolt removal tool that is operable from a conventional compressed air supply.
A disadvantage associated with using such prior art liner bolt removal tools to remove conventional liner bolts, is that it is necessary for the operator of the removal tool be assisted by a workman who helps align the moil of the removal tool with the liner bolt. This is because even though the removal tools are suspended, their size and weight makes them difficult to handle and they obstruct the operator's view of the work area. The workman assisting the operator typically utilizes a handheld moil guide as shown in FIG. 1 of this specification. This places the workman assisting the operator of the liner bolt removal tool at risk of injury, due to his proximity to the working end of the tool as it is aligned with the liner bolt.
Another disadvantage of removing liner bolts using these liner bolt removal tools is the damage caused to the mill casing in the area around the bolt hole, as a result of misalignment.
The present invention seeks to overcome at least some of the abovementioned disadvantages.